In the manufacture of cotton yarn, a sliver is normally prepared by forming a web of fibers from individual fibers, by working the web to align and refine the fibers, by forming the web into a sliver, and by coiling the sliver. The sliver is subsequently drawn out and twisted to form the yarn. The working of the web is done in a textile card, and the web must be as thin as possible and must be handled carefully because it is so thin and fragile. The web enters the carding machine at the feed roll, passes to a licker-in, to the main cylinder, is doffed from the main cylinder at the doffing cylinder, is combed from the doffing cylinder and passed through a trumpet where it is formed into a sliver. The sliver moves from the trumpet through various calendering rolls and guides to a coiler head and a coiler can where the sliver is coiled and temporarily stored. The web and sliver are very fragile, and it is difficult to form and maintain the web and sliver during the initial start-up of the card. Because it is difficult to start the card, the speed of rotation of the doffing cylinder is preferably variable with respect to the speed of rotation of the main cylinder so that the doffing cylinder can be operated at a slow speed of rotation during start-up of the system to produce a thick, strong web which can be handled without tearing when taken from the doffing cylinder and passed through the trumpet and to the coiler can. After the start-up of the card has been completed, the speed of rotation of the doffing cylinder can be increased with respect to the speed of rotation of the main cylinder, thus further working and drawing out the web.
At the present time, many of the cards in operation are operated at a constant speed. In order to prevent the web or sliver from tearing or breaking during the start-up, the carding machines are operated at a relatively slow speed. Although the slow speeds allow continuous production of the sliver with relatively few machine shut-downs due to breakage of the web or sliver, the overall production rate of the sliver is slow, and therefore unsatisfactory. While some carding machines include means for varying the doffing cylinder speed with respect to the main cylinder speed, when the prior art systems are turned off, the driving belt and other elements associated with the system cause the doffing cylinder to continue rotating before the system is completely stopped. In addition, the present carding systems which do include variable speed doffing cylinders usually require the card operator to manually change the speed of the doffing cylinder, and if the operator fails to change the speed of the doffing cylinder promptly after start-up, the web is not properly worked.